From dc0e9bcc5866e58da8cce0d4076b5b8f91fd8277 Mon Sep 17 00:00:00 2001
From: Adarsh Das <adarshdas950@gmail.com>
Date: Tue, 16 Jun 2026 23:51:04 +0530
Subject: [PATCH] Implement huge page for Continuation and Continuation
 correction history

STC SMP
Elo   | 2.31 +- 1.85 (95%)
SPRT  | 5.0+0.05s Threads=8 Hash=256MB
LLR   | 2.91 (-2.25, 2.89) [0.00, 4.00]
Games | N: 32202 W: 8023 L: 7809 D: 16370
Penta | [32, 3587, 8667, 3765, 50]
https://recklesschess.space/test/15269/

Bench: 3204302
---
 src/history.rs | 76 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 72 insertions(+), 4 deletions(-)

diff --git a/src/history.rs b/src/history.rs
index bd879600b..b8aa4c613 100644
--- a/src/history.rs
+++ b/src/history.rs
@@ -6,6 +6,74 @@ type FromToHistory<T> = [[T; 64]; 64];
 type PieceToHistory<T> = [[T; 64]; 13];
 type ContinuationHistoryType = [[[[PieceToHistory<i16>; 64]; 13]; 2]; 2];
 
+struct HugeBox<T> {
+    ptr: std::ptr::NonNull<T>,
+}
+
+unsafe impl<T: Send> Send for HugeBox<T> {}
+unsafe impl<T: Sync> Sync for HugeBox<T> {}
+
+impl<T> HugeBox<T> {
+    fn new_zeroed() -> Self {
+        #[cfg(target_os = "linux")]
+        let ptr = unsafe {
+            use libc::{MADV_HUGEPAGE, MAP_ANONYMOUS, MAP_FAILED, MAP_PRIVATE, PROT_READ, PROT_WRITE, madvise, mmap};
+            let size = std::mem::size_of::<T>();
+            assert!(size > 0, "HugeBox requires a non-zero-sized type");
+            let p = mmap(std::ptr::null_mut(), size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+            if p == MAP_FAILED {
+                std::alloc::handle_alloc_error(std::alloc::Layout::new::<T>());
+            }
+            madvise(p, size, MADV_HUGEPAGE);
+            std::ptr::NonNull::new_unchecked(p.cast::<T>())
+        };
+
+        #[cfg(not(target_os = "linux"))]
+        let ptr = unsafe {
+            let layout = std::alloc::Layout::new::<T>();
+            let p = std::alloc::alloc_zeroed(layout);
+            if p.is_null() {
+                std::alloc::handle_alloc_error(layout);
+            }
+            std::ptr::NonNull::new_unchecked(p.cast::<T>())
+        };
+
+        HugeBox { ptr }
+    }
+}
+
+impl<T> std::ops::Deref for HugeBox<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { self.ptr.as_ref() }
+    }
+}
+
+impl<T> std::ops::DerefMut for HugeBox<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { self.ptr.as_mut() }
+    }
+}
+
+impl<T> Drop for HugeBox<T> {
+    fn drop(&mut self) {
+        #[cfg(target_os = "linux")]
+        {
+            let size = std::mem::size_of::<T>();
+            assert!(size > 0, "HugeBox requires a non-zero-sized type");
+            unsafe {
+                libc::munmap(self.ptr.as_ptr().cast(), size);
+            }
+        }
+
+        #[cfg(not(target_os = "linux"))]
+        unsafe {
+            let layout = std::alloc::Layout::new::<T>();
+            std::alloc::dealloc(self.ptr.as_ptr().cast(), layout);
+        }
+    }
+}
+
 fn apply_bonus<const MAX: i32>(entry: &mut i16, bonus: i32) {
     let bonus = bonus.clamp(-MAX, MAX);
     *entry += (bonus - bonus.abs() * (*entry) as i32 / MAX) as i16;
@@ -101,7 +169,7 @@ impl Default for CorrectionHistory {
 
 pub struct ContinuationCorrectionHistory {
     // [in_check][capture][piece][to][piece][to]
-    entries: Box<ContinuationHistoryType>,
+    entries: HugeBox<ContinuationHistoryType>,
 }
 
 impl ContinuationCorrectionHistory {
@@ -125,13 +193,13 @@ impl ContinuationCorrectionHistory {
 
 impl Default for ContinuationCorrectionHistory {
     fn default() -> Self {
-        Self { entries: zeroed_box() }
+        Self { entries: HugeBox::new_zeroed() }
     }
 }
 
 pub struct ContinuationHistory {
     // [in_check][capture][piece][to][piece][to]
-    entries: Box<ContinuationHistoryType>,
+    entries: HugeBox<ContinuationHistoryType>,
 }
 
 impl ContinuationHistory {
@@ -155,7 +223,7 @@ impl ContinuationHistory {
 
 impl Default for ContinuationHistory {
     fn default() -> Self {
-        Self { entries: zeroed_box() }
+        Self { entries: HugeBox::new_zeroed() }
     }
 }